1. Field of the Invention
The present invention relates to a patterned substrate for gallium nitride-based light emitting diode and the light emitting diode using the same. The present invention can provide the optimization of the patterns in the patterned substrate.
2. Discussion of Related Art
Light-emitting diodes (LEDs) have attracted much attention as light sources for applications such as indicator lights on devices, traffic lights, automobile lighting, and indoor and outdoor lighting, including street lighting. This is due to their low energy consumption, long lifetime, robustness, absence of a warm-up period, favorable controllability, and good color rendering. To include a wider range of applications, improvements in the efficiencies of LEDs are required.
The light-extraction efficiency (LEE) of LEDs is an important parameter. The LEE of an LED is defined as the ratio of the number of photons emitted into free space from an LED chip to the number of photons emitted from the active region inside the LED chip. It is limited by total internal reflection inside the LED semiconductor chip, which typically has a larger refractive index than the surrounding material.
When the light generated from the active region inside the semiconductor is incident upon the interface between the semiconductor and the surrounding space, if the angle of the emitted light exceeds the critical angle, TIR occurs and light is trapped inside the semiconductor, eventually being dissipated as heat. The LEE of an LED is typically small, because there is a large difference in refractive index between the semiconductor and the surrounding space. For example, the refractive index of gallium nitride (GaN) is 2.5, and the LEE of a GaN-based LED chip with a simple rectangular shape into free space is only 4%.
Numerous approaches have been used to improve the LEE, including the patterned sapphire substrates (PSSs). For example, Korean published patent application No. 2012-84839 is reported. PSSs employ arrayed patterns on the entire top surface of the sapphire that forms the LED substrate. Scattering and multiple reflection of the light inside the LED chip can be enhanced with these structures, breaking the TIR condition and therefore improving the LEE. The PSS can also serve to reduce the threading-dislocation density during the growth of LED epitaxial layers.
However, there are still a lot of requirement for improving the quality of patterned substrate.